[Comparison of edge fitness and metal-ceramic bonding force of base metal crowns performed using two methods]

To compare the marginal fitness and metal-ceramic bonding strength between laser printing metal crown and cast cobalt-chromium alloy crown.

Cobalt-chromium alloy crowns (n=10)(group A) were made by laser printing and another 10 by traditional casting (group B), respectively. All the first molar crowns were metal substitutes, and the basal crowns were placed in the standard substitutes. The marginal fitness of the basal crown was assessed by observing the margin of the basal crown and the shoulder gap of the substitution under stereomicroscope. Shear test of the basal crown was carried out by universal tester to evaluate the bonding strength between the metal and the porcelain. The differences of the marginal fitness and the bonding strength between the two methods of making basal crown were compared. SPSS 25.0 sofware package was used to analyze the data.

The gap between the metal base crown and the generation shoulder of group A was significantly smaller than that of group B[（48.52±5.26)μm vs (76.25±8.37)μm, P<0.05]. The intensity was significantly higher than that of group B [（11.35±3.29）N vs （7.24±2.07）N, P<0.05]. Under electron microscope, the metal layer of group A was more closely combined with the porcelain layer.

The marginal fitness and bonding strength of metal base crowns made by laser printing and traditional casting methods are acceptable. Laser printing metal base crowns have better marginal fitness and stronger bonding strength between metal and porcelain, which is an ideal technology for metal base crowns.